Evolution in Real Time

Basic Evolutionary Principles and Natural Selection

  • Evolution can be observed and measured in real-time, not just as a slow, gradual process.

  • Lecture Outline:

    • Basic evolutionary principles and natural selection.
    • Classic case studies (peppered moths, finches, guppies).
    • Examples of evolution affecting modern humans (cappuccinos to COVID).

Explaining Biological Complexity

  • The human eye as an example of complex biological structures.

  • The eye's component parts work in an integrated way to bring light into the retina.

  • Photoreceptors (rods and cones) convert light information into a format the brain can interpret.

  • Before evolutionary framework, theologians and philosophers used divine creation to explain such complexity.

Teleological Argument

  • Teleo: end result; ology: study of.

  • Focuses on the end result of design and its function, ignoring the origins of complexity.

  • Reverend William Paley argued for a divine creator based on complexity (e.g., the human eye).

  • Analogy: Finding a watch on a beach implies a creator due to its complex design and function.

Natural Selection

  • Richard Dawkins: complex structures like the eye can arise through random chance and natural selection.

    • Book: "The Blind Watchmaker" addressing Paley's arguments about intelligent design.

  • Natural selection is a blind process with no direction or intended end result.

  • Each stage has advantages/disadvantages; natural selection chooses among the outcomes.

Charles Darwin and Alfred Wallace

  • Darwin and Wallace independently proposed the theory of natural selection in 1859.

  • Darwin is more famous due to his extensive work "On the Origin of Species".

Defining Evolution

  • Evolution: descent with modification

    • Successive generations are modified through natural selection.

  • People knew about evolution before Darwin.

    • Domestication, farming, breeding pigeons.
    • Mechanism of natural selection was key to success.

Defining Natural Selection

  • Natural selection: differential survival and reproduction of individuals due to differences in phenotype.

  • Phenotype: observable traits (behavior, morphology, life history traits).

  • Variation in traits affects the success of an organism.

Key Ingredients for Natural Selection

  • Variation: phenotypic traits must vary.

    • Example: color patterns in male guppies.

  • Fitness consequences: variation must affect survival and reproduction.

  • Heritability: traits must be passed to offspring.

Adaptation

  • Adaptation is a consequence of natural selection.

  • Example: giraffe's neck length evolving to reach higher branches.

  • Recap: variation, fitness effects, heritability lead to evolutionary change.

Classic Case Studies

Peppered Moths

  • Classic example of evolutionary change.

  • Variation in color (light and dark forms).

  • Until the early 1900s, the white form was predominant (unmelanized).

  • Industrial Revolution led to more soot, turning trees black.

  • White moths became visible to predators; black moths had an advantage.

  • Shift in predominant color to the black form.

  • Clean Air Act cleaned the environment; shift back to the unmelanized form.

  • Evolution can happen quickly when selection pressure is strong.

Darwin's Finches

  • Darwin observed variation in beak shape among finches in the Galapagos Islands.

  • Hypothesized that beak shape differences were due to food availability.

  • Soft seeds/insect prey: smaller beaks; harder seeds: larger beaks.

Peter and Rosemary Grant's Research

  • Studied beak variation in finches on Daphne Major in the 1970s.

  • 1977 drought: small, soft seeds unavailable.

  • Rapid shift in beak size tracked the environmental change.

  • Birds with larger beaks survived in the harsh environment.

  • 1983 El Nino event (flooding): small seeds became abundant.

  • Larger beaks became a disadvantage.

  • Beak size tracked seed abundance: x axis: time y axis: beak measurement

Guppies

  • John Endler studied guppies in Trinidad to understand competing forces of natural and sexual selection.

Sexual Selection

  • Sexual dimorphism: differences in phenotypic traits between sexes.

  • Guppies: males are colorful and small; females are larger and drab.

  • Darwin: sexual selection focuses on reproduction.

  • Selection targets males, with females choosing colorful males.

  • Traits favored by sexual selection (bright colors) can decrease survival.

  • Sexual selection acts against natural selection.

Observational Study

  • Guppies above waterfalls were more colorful than those below.

  • Main predator (pike cichlid) existed below waterfalls but not above.

  • Hypothesis: relaxed predation allows males to be more colorful to attract mates.

Experimental Study

  • Transplanted guppies from low predation site to high predation.

  • Measured guppies over time. X axis: C=original site dangerous locality, R= after two years of introduction to safe site, X= two years after instruction to a site with no guppies.

  • Males became more conspicuous when predation was relaxed.

  • Evolutionary change occurred over just four years (12 guppy generations).

Lab Experiment with Ponds

  • Endler controlled elevation, light levels, and backgrounds.

  • Results matched field experiment: guppies in low-predation environments became more colorful.

  • Rivulous with the rivulous r is the rivulous ponds. K here is no predator at all, and C are the dangerous ones.

  • Evolutionary change was 10,000 to 10,000,000 times faster than observed in the fossil record.

Evolution Affecting Humans

Lactose Tolerance

  • Most adults are lactase tolerant after weaning.

  • Babies produce lactase to break down sugars in mother's milk.

  • Mammals lose the ability to produce lactase after weaning.

  • Humans: agricultural revolution and domestication of cattle led to selection pressure for lactose tolerance.

  • Individuals with the trait to tolerate any lactose had a strong evolutionary advantage.

  • LCT gene codes for lactase; mutations enable lactose processing.

Global Distribution

  • Populations with dairy farming have increased lactose tolerance.

  • Independent evolution across societies that exploited milk.

  • Massai, tutsi, east africa, northern europe, middle east have lactose tolerance.

  • Mongolia ferments milk, so no lactose selection pressure.

Antibiotic Resistance

  • Antibiotic use imposes selection pressure on bacteria.

  • Resistant bacteria survive and reproduce.

  • Over time, the population is dominated by a resistant strain.

MRSA

  • Staphylococcus aureus evolved to resist methicillin.

Evolution of Viruses

  • COVID-19 and SARS-CoV-2

  • Use online tools (nextstrain.org) to track real-time evolution.